Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $194.31   6.306%   $206.5632   $206.56   $206.55   $206.60  
  Purchase #2 $249.96   12.853%   $282.0874   $282.09   $282.10   $282.10  
  Purchase #3 $156.25   11.161%   $173.6891   $173.69   $173.70   $173.70  
  Purchase #4 $149.33   13.855%   $170.0197   $170.02   $170.00   $170.00  
  Purchase #5 $205.54   7.750%   $221.4694   $221.47   $221.45   $221.50  
  Purchase #6 $51.54   6.640%   $54.9623   $54.96   $54.95   $55.00  
  Purchase #7 $146.48   8.629%   $159.1198   $159.12   $159.10   $159.10  
  7 purchase totals = $1,153.41       $1,267.9109   $1,267.91   $1,267.85   $1,268.00